Our oil-fired furnace (Thermo Pride)used to be fed from an underground tank and was set-up for a two-line system. Due to some construction, that tank was no longer available so I installed an above ground tank outside and opted to use a single line to the furnace. After removing the set-screw from the return port of the fuel pump (and installing a plug), I ran a new 3/8" copper feed-line to the new tank.

After doing so, the fuel pump began making a "whining" noise while running but was especially noticable (annoying!) at start-up and shut-down. At shut-down, my best description would be that the noise was similar to a jet turbine winding down. After several weeks, curiosity led me to place a 5 gallon bucket next to the furnace and convert the pump back to a two-line system to feed from it. QUIET AS A MOUSE, so I bought another roll of tubing and installed it as a return-line to the outside tank, only to find the noise had returned, although in a somewhat different pitch.

Filling the 5 gallon bucket next to the furnace and using it as a "fuel tank" is my short term option but I don't foresee having to do it again next year. Any suggestions would be appreciated!